NASA-Funded Scientists Discover Tenth Planet

This time-lapse image of a newfound planet in our solar system, called 2003UB313, was taken on Oct. 21, 2003, using the Samuel Oschin Telescope at the Palomar Observatory near San Diego, Calif. The planet, circled in white, is seen moving across a field of stars.+ See more images+ Quicktime (CC): Narrated overview of discovery

A planet larger than Pluto has been discovered in the outlying
regions of the solar system.

The planet was discovered using the Samuel Oschin Telescope at Palomar
Observatory near San Diego, Calif. The discovery was announced today by
planetary scientist Dr. Mike Brown of the California Institute of
Technology in Pasadena, Calif., whose research is partly funded by NASA.

The planet is a typical member of the Kuiper belt, but its sheer size in
relation to the nine known planets means that it can only be classified
as a planet, Brown said. Currently about 97 times further from the sun
than the Earth, the planet is the farthest-known object in the solar
system, and the third brightest of the Kuiper belt objects.

"It will be visible with a telescope over the next six months and is
currently almost directly overhead in the early-morning eastern sky, in
the constellation Cetus," said Brown, who made the discovery with
colleagues Chad Trujillo, of the Gemini Observatory in Mauna Kea,
Hawaii, and David Rabinowitz, of Yale University, New Haven, Conn., on
January 8.

Brown, Trujillo and Rabinowitz first photographed the new planet with
the 48-inch Samuel Oschin Telescope on October 31, 2003. However, the
object was so far away that its motion was not detected until they
reanalyzed the data in January of this year. In the last seven months,
the scientists have been studying the planet to better estimate its size
and its motions.

"It's definitely bigger than Pluto," said Brown, who is a professor of
planetary astronomy.

Scientists can infer the size of a solar system object by its
brightness, just as one can infer the size of a faraway light bulb if
one knows its wattage. The reflectance of the planet is not yet known.
Scientists can not yet tell how much light from the sun is reflected
away, but the amount of light the planet reflects puts a lower limit on
its size.

"Even if it reflected 100 percent of the light reaching it, it would
still be as big as Pluto," says Brown. "I'd say it's probably one and a
half times the size of Pluto, but we're not sure yet of the final size.

"We are 100 percent confident that this is the first object bigger than
Pluto ever found in the outer solar system," Brown added.

A name for the new planet has been proposed by the discoverers to the
International Astronomical Union, and they are awaiting the decision of
this body before announcing the name.